Add SpMcRingBuffer to base class StimulusBuffer

This will hopefully genericise the interface for Stimbuffs.

include/user/sequenceLock.h

@@ -20,6 +20,14 @@ public:
 	: sequenceNo(0)
 	{}
 
+	~SequenceLock() = default;
+
+	// Non-copyable, non-movable (std::atomic is neither copyable nor movable)
+	SequenceLock(const SequenceLock&) = delete;
+	SequenceLock& operator=(const SequenceLock&) = delete;
+	SequenceLock(SequenceLock&&) = delete;
+	SequenceLock& operator=(SequenceLock&&) = delete;
+
 	/* Atomically increments sequenceNo and issues a release barrier.
 	 * Makes the sequence number odd, indicating a write is in progress.
 	 */